How Body Age Works
Body Age is a wellness estimate based on recent sleep, activity, and fitness signals. It is designed to make longer-term patterns easier to understand. It is not a diagnosis and does not judge your health from a single day.
Seven Metrics, Three Dimensions
| Dimension | Metrics |
|---|---|
| Sleep | Sleep duration and sleep regularity |
| Activity | Aerobic duration, high-intensity duration, and daily steps |
| Fitness | VO2 max and resting heart rate |
Each available metric is scored using its current in-app rule. The metrics are combined within their dimension, converted to an age adjustment, and then combined with actual age. Missing metrics are excluded instead of being replaced with guessed values.
How to Read Aging Rate
Aging rate is a separate trend estimate. It uses the robust trend of the stable Body Age difference over the most recent 30 days. Around 1x means the difference is broadly stable; below 1x means it is moving younger, and above 1x means it is moving older. The displayed range is 0–3x.
This is not a week-over-week change rate. Use the trend interpretation below the gauge to understand whether the recent Body Age difference is improving, stable, or needs attention.
Data Windows and Availability
- Stable Body Age uses up to 180 calendar days with a 45-day exponential half-life. Sleep duration and resting heart rate use daily representatives; regularity and activity use trailing seven-day features.
- VO2 max uses a representative recent value from a 30-day window.
- The first estimate needs at least 21 valid days and two available dimensions. Data is marked as accumulating below 21 days, warming up from 21–89 days, and mature at 90 days or more. Mature means sufficient history, not clinical calibration.
- Aging rate is withheld until at least 21 valid trend points are available.
- At least two of the three dimensions must be available before Body Age is shown.
The current day's steps, resting heart rate, and workout minutes receive lower quality until that natural day is complete. A published result is refreshed every three natural days, while the 180-day scoring window continues to move forward.
Apple Health permissions, Apple Watch wear time, source priority, battery, and recent sample availability can affect which metrics are included.
Missing Data
A missing metric does not receive a zero and is not estimated. Yuelu recalculates the available weights so incomplete data does not unfairly dominate the result. If too few dimensions are available, the page reports insufficient data instead of producing a Body Age.
Health Notice
Body Age and aging rate are for wellness education and product explanation only. They are not medical diagnoses or treatment advice. Consult a qualified clinician for persistent symptoms or health concerns.